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1 /* -*- c-basic-offset: 4 indent-tabs-mode: nil -*- vi:set ts=8 sts=4 sw=4: */
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2 /*
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3 QM DSP Library
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4
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5 Centre for Digital Music, Queen Mary, University of London.
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6 This file by Chris Cannam.
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7
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8 This program is free software; you can redistribute it and/or
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9 modify it under the terms of the GNU General Public License as
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10 published by the Free Software Foundation; either version 2 of the
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11 License, or (at your option) any later version. See the file
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12 COPYING included with this distribution for more information.
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13 */
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14
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15 #ifndef RESAMPLER_H
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16 #define RESAMPLER_H
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17
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18 #include <vector>
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19
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20 /**
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21 * Resampler resamples a stream from one integer sample rate to
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22 * another (arbitrary) rate, using a kaiser-windowed sinc filter. The
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23 * results and performance are pretty similar to libraries such as
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24 * libsamplerate, though this implementation does not support
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25 * time-varying ratios (the ratio is fixed on construction).
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26 *
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27 * See also Decimator, which is faster and rougher but supports only
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28 * power-of-two downsampling factors.
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29 */
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30 class Resampler
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31 {
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32 public:
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33 /**
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34 * Construct a Resampler to resample from sourceRate to
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35 * targetRate.
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36 */
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37 Resampler(int sourceRate, int targetRate);
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38
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39 /**
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40 * Construct a Resampler to resample from sourceRate to
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41 * targetRate, using the given filter parameters.
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42 */
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43 Resampler(int sourceRate, int targetRate,
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44 double snr, double bandwidth);
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45
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46 virtual ~Resampler();
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47
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48 /**
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49 * Read n input samples from src and write resampled data to
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50 * dst. The return value is the number of samples written, which
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51 * will be no more than ceil((n * targetRate) / sourceRate). The
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52 * caller must ensure the dst buffer has enough space for the
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53 * samples returned.
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54 */
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55 int process(const double *src, double *dst, int n);
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56
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57 /**
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58 * Return the number of samples of latency at the output due by
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59 * the filter. (That is, the output will be delayed by this number
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60 * of samples relative to the input.)
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61 */
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62 int getLatency() const { return m_latency; }
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63
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64 /**
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65 * Carry out a one-off resample of a single block of n
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66 * samples. The output is latency-compensated.
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67 */
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68 static std::vector<double> resample
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69 (int sourceRate, int targetRate, const double *data, int n);
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70
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71 private:
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72 int m_sourceRate;
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73 int m_targetRate;
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74 int m_gcd;
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75 int m_filterLength;
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76 int m_bufferLength;
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77 int m_latency;
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78 double m_peakToPole;
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79
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80 struct Phase {
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81 int nextPhase;
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82 std::vector<double> filter;
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83 int drop;
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84 };
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85
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86 Phase *m_phaseData;
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87 int m_phase;
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88 std::vector<double> m_buffer;
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89 int m_bufferOrigin;
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90
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91 void initialise(double, double);
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92 double reconstructOne();
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93 };
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94
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95 #endif
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96
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